Radar.
Large objects can be detected from the ground or from the space station, and the station is moved out of the way.
The space station and the shuttle are designed to take hits from objects too small to detect from radar and still survive.
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...Larger particles (objects greater than 10-cm in diameter) are being tracked and catalogued by USSPACECOM radar. Spacecraft and satellites can avoid collisions by maneuvering around the larger debris. For example, when a space shuttle is in orbit, the USSPACECOM regularly examines the trajectories of orbital debris to identify possible close encounters. If a catalogued object is projected to come within a few kilometers of the space shuttle, it will normally maneuver away from the object.
Particles less than 1 mm in diameter are not tracked by radar. Fortunately, small particles pose less of a catastrophic threat but they do cause surface abrasions and microscopic holes to spacecraft and satellites.
The greatest challenge is medium size particles (objects with a diameter between 1 mm to 10 cm) because they are not easily tracked and are large enough to cause catastrophic damage to spacecraft and satellites.
Why simulate particle impacts on spacecraft?
Spacecraft must be designed to withstand hypervelocity impacts by untrackable particles. Conducting hypervelocity impacts on spacecraft and satellite components assesses the risk of orbital debris impacting operating spacecraft and satellites. Developing new materials and designs from HVI impact data provides a better understanding to protect spacecraft and satellites from the debris in the space environment.
One concept of spacecraft shielding recently developed, termed multishock, uses several layers of lightweight ceramic fabric to act as "bumpers," which repeatedly shock a projectile to such high energy levels that it melts or vaporizes before it can penetrate a spacecraft's walls. Lightweight shields based on this concept are used on the International Space Station (ISS)....